1. Field of the Invention
This invention relates to a method for use in oilfield and pipeline operations to monitor and control emulsion formation in formation fluids. This invention particularly relates to a method for monitoring and controlling emulsions originating from formation fluids located downhole or contained in pipelines, free water knock-outs and other separation equipment.
2. Background of the Art
Fluids that are typically first recovered from a wellbore in oilfield recovery operations generally consist primarily of crude oil and water. Such fluids are referred to herein as “formation fluids”. These fluids may also contain a number of additional components, such as water insoluble materials in the form of colloidal suspensions, but these are generally very minor components. Thus, one of the first steps in recovery of the oil fraction, which is often a primary goal of such recovery operations, is to separate the oil from the water. This step substantially reduces the volume of material that must undergo further processing and also simplifies further processing of the oil.
Fortunately, water and oil are not miscible and tend to separate into two distinct phases. In order to capitalize on this natural tendency, those skilled in the art of oil recovery operations employ vessels wherein the formation fluid can stand for a period of time. These vessels are designated as “free water knock-outs”. The separation results in a distinct water layer at the lowest vessel level; a distinct oil layer at the uppermost vessel level; and an interface between the two which constitutes an emulsion, i.e., a dispersion of oil and water droplets, often with one component predominating as a continuous phase, and the other phase predominating as a discontinuous phase. This emulsion layer is often alternatively referred to as the “rag layer”. The separated oil and water can be easily removed from the free water knock-out, but it is desirable to ensure that the emulsion layer remain in the free water knock-out where it cannot contaminate either of the recovered oil or water products.
Furthermore, considering the scale of oil recovery operations, it is not surprising that the rag layer is often substantial and, therefore, contains a considerable amount of economically valuable recovered oil product. Thus, it is desirable to quantitatively reduce this layer as much as possible in order to optimize oil recovery. Such reduction effort can include addition of demulsification additives such as alkyl phenol resins, e.g., oxy-alkyl phenol resins. Since a certain amount of emulsification results from the increased shear of higher pump rates, it is also possible to reduce emulsification by reducing pump rate.
Previously, significant demulsification has often been difficult. This is, in part, simply because inflow and outflow from the free water knock-out are typically maintained continuously. During the process the oil is recovered from an upper oil outflow pipeline and the water is recovered from a lower water outflow pipeline. Such outflow piping, designed for simple decantation, obviously does not distinguish between the three layers. The result is that some of the emulsion layer can easily creep in with the oil-only layer and/or with the water-only layer during the separation process.
In view of difficulties in obtaining relatively pure decantation products, it would be desirable in the art to find a way to easily detect and identify emulsion in a formation fluid, whether such emulsion is present as a discrete emulsion, or “rag”, layer in a free water knock-out or at another point in the transport of a formation fluid. The ability to identify emulsion could then be used to enable control of the emulsion, including reduction of contamination of decantation products and/or effective demulsification.